The United States Secretary of State Mike Pompeo on Thursday said his country had concluded that the regime of President Bashar al-Assad used chlorine as a chemical weapon in Syria on May 19.

According to Pompeo, a U.S. intelligence assessment found that Syrian government forces had violated the international accord banning chemical weapons in warfare.

The statement by the Secretary of State is aimed at dissuading the Assad government from using chemical weapons on the battlefield.

Syria joined the chemical weapons treaty in 2013, which prohibits the development, production and use of poisonous gases in war. The production of chlorine, which also has civilian applications, is not banned by the treaty, but its use in the battlefield is prohibited by the convention.

France and the U.K. are also expected to issue statements on the latest findings.

Syria descended into war almost eight years ago, sparked by protests against the president. The war has killed more than 300,000 people and forced millions to flee their homes.

The United Nations earlier this year called upon the warring factions to engage in dialogue as a way of ending the protracted war.